Feathers as a Source of Fibers

Harold P. Lundgren.

Feathers have often been suggested as raw materials for synthetic fibers. They are fibrous in structure. They are tough. They are practically pure protein, which is the stuff from which other fibers wool, silk, and hair are made. The chief interest in feathers lies in their availability an estimated 120 million pounds a year, which are mostly wasted, mainly because suitable ways are lacking for converting them into useful products.

The main difficulty in handling feathers has been their insolubility in common solvents. That is typical of the keratins, the class of proteins that make up the protective covering of animals wool, hair, and skin as well as the feathers on birds. Actually, that property would be desirable if the material were in the form of a usable fiber, but the feathers have to be in solution, or at least in a highly swollen condition, in order to extrude the fibers.

Feathers can be dissolved in strong caustic solutions, but that treatment is so harsh that the final units, the threadlike molecules, are broken into small pieces. As a result, anything that resembles a true fiber cannot be made from such material the extruded thread, when dried, simply crumbles to a dust.

We have to find a less drastic treatment. That has been a major research problem, one that we have not yet solved completely.

In his search for appropriate agents and conditions for handling feathers, the chemist has learned that the characteristic inertness of feathers is chiefly the manifestation of certain chemical cross-links, or bonds, that tie the long, threadlike molecules into the natural, netlike structure.

Such hooking together of threadlike molecules occurs in other proteins, too, but in feathers the interaction is firmer. From his knowledge of the nature of these cross-links, the chemist can choose specific chemical agents that selectively sever them without destroying the other bonds that connect the atoms into long threads. In other words, the chemist, in tearing apart the feather, seeks to preserve the natural threadlike units, for they are the building blocks required to make synthetic fibers.

The long molecular chains can be separated by use of water solutions of a mixture of a salt ( sodium bisulfite) and a detergent, one type of which is made from kerosene and sulfuric acid. The mixture of sodium bisulfite and detergent, acts simultaneously on the feathers to break the sulfur bonds, as well as salt bonds and hydrogen bonds, all of which help to stabilize the natural network. This reacting mixture is mild compared to caustic soda, which breaks the cross-links of the fiber network and the long chains. As soon as the bisulfite and detergent mixture acts, the molecules come apart and dissolve in the water solution.

The dissolved threadlike molecules, however, are not just feather protein alone. Some of the detergent molecules have attached themselves chemically edgewise to them.

That union; which is a rather loose one, has proved of special advantage for the manipulation of the feather material into fibers. The attached detergent helps to unfold the flexible, coiled-up, threadlike molecules. In that way, the molecules are lined up more readily when the solutions are forced through the tiny openings of the spinning nozzle. The alinement of the molecules is easily detected by special optical methods.

When the sirupy stream of lined-up molecules oozing through the spinning nozzle strikes a precipitating solution of salt, the feather molecules immediately congeal to form a fiber they begin to form a new net structure. The newly formed fiber is highly elastic and weak. Extensive network formation, or rehooking of the protein molecules, is necessary before the fiber acquires appreciable strength, but that is not possible until the detergent molecules are removed. The detergent ( which by now has served its purpose as an agent to help separate the protein molecules and then to keep them apart and straightened out until fiber formation has begun) is in the way and prevents extensive interaction. It can be removed by washing the fibers with solutions of acetone in water. This solvent combination breaks the rather loose union between the detergent and feather protein, and the solvent then extracts the detergent. The fiber is left as essentially pure protein. When the extracted fiber is stretched, the chains interact further, with corresponding increase in strength of the fiber.

A METHOD OF PREPARING BRISTLES from feathers, developed at the Western Regional Research Laboratory, is based on a new method for recovery of keratin. Instead of using synthetic detergents, we employ a simplified process having mixtures of alcohol and water as the solvent. When feathers are heated with this mixture at suitably high temperatures, about 70 percent of the protein dissolves. It is easily recovered as a dry powder. Bristles can be made by moistening the powder with the solvent and extruding the material at high temperatures through small openings.

The highly stretched keratin fibers from feathers are comparatively strong when dry even stronger than wool. They also have a true fiber structure like wool, as revealed by X-ray pictures. But they suffer from a weakness that is characteristic of synthetic fibers made from proteins; they lack the resistance to water that is desired for a good textile fiber. The weakness can be overcome somewhat by treatment with chemical curing agents, such as formaldehyde and acetic anhydride, but in no case has it been possible to bring the wet strength up to more than half of the dry value. We have been unable to achieve the degree of cross-bonding of the chains found in the original feather.

Another limiting property of the fibers made from feathers is their low elasticity. They are not so elastic as the fibers made from casein and zein. But the keratin fibers do exhibit at least one unique characteristic a close resemblance to hair. That characteristic suggests possible application of them for such comparatively minor purposes as mannequin wigs and as a component of various decorative fabrics. Such fabrics have potential use as suiting interlinings or oil filters.

A further disadvantage of the keratin fibers is their color. Feather pigments are intimately associated with the protein and are not removed in the processing. In consequence, the fibers carry the color of the feathers used, and the output of general-purpose fibers is limited to white feathers.

The biggest problem ahead is to cut the relatively high cost of the process. The need to extract and recover the detergent makes that procedure somewhat more costly than the methods adequate for casein and zein. Unless we can find easier ways to carry out the operations, the only use of the fibers is most likely to be in specialty items like brush bristles, wigs, insulation, and decoration. For the time being, then, technicians are acquiring more information on the molecular structure of the fibers and new methods for stabilizing the fibers toward water. It may yet be practical to use feathers for making a general-purpose fiber.

HAROLD P. LUNDGREN is in charge of the wool section of the protein division, Western Regional Research Laboratory. He joined the Laboratory in 1941; previously, he was a research associate in the University of Wisconsin and a post-doctorate research fellow in the University of Upsala, Sweden. Dr. Lundgren is a graduate of North Dakota State College and the University of Minnesota.

THE AMOUNT of water in any biological material may soon be measured by push-button electronic methods. Electrical methods for the determination of moisture are widely used because of their speed and because they do not alter the specimen being measured. Oven methods, by contrast, are time-consuming and alter biological substances so profoundly as to render them unfit for further use.

A new instrument to extend the range of electrical methods is being perfected. Existing instruments are inaccurate or fail entirely if the material under test contains more than about 20 percent water. As biological materials may consist of 90 percent water or more, application of electrical methods is limited.

The new instrument makes use of one of the most recent findings of nuclear physics. In 1946, physicists at Harvard University and Stanford University independently developed methods for measuring the magnetic energy absorbed by the nuclei of certain atoms in liquids and solids. Previously that had been done only for gases and vapors. The work at Harvard and Stanford showed that if water is placed in a magnetic field, the hydrogen nuclei in the water can absorb radio waves of a specific frequency, much as a radio receiver accepts only the waves from the station to which it is tuned. Tuning for the hydrogen nuclei is accomplished by adjusting the strength of the magnetic field to which they are subjected.

The ability of the hydrogen nuclei to absorb radio-frequency (rf) energy is utilized in the instrument which is being developed at the Western Regional Research Laboratory to measure the water content of agricultural materials. The instrument contains electronic circuits arranged to measure the rf energy absorbed by the hydrogen nuclei in a specimen of a water-containing substance. Allowance is made for the energy absorbed by the hydrogen nuclei in the non-aqueous components of the specimen by means of calibration measurements on the materials for which the instrument is intended. The calibrations become a part of the instrument and serve to relate the amount of energy absorbed to the moisture content of the material. Once the instrument is calibrated, the moisture content of a specimen containing an unknown amount of water can be found in the few minutes required to prepare the sample and read the instrument.

Preliminary trials on fruits and vegetables show that this new method can be used over the entire range of moisture encountered in natural or modified biological systems. T. M. Show, Western Regional Research Laboratory.